The purpose of this research is: 1. Describe the anoxic-induced alterations in the kinetics of cation exchange across the cell membranes. 2. Elucidate the alterations in basic cellular and membrane mechanisms responsible for the altered kinetics, and 3. Relate these to the changes in cellular electrical activity, metabolism, and mechanical performance observed in the heart during anoxia. This will be accomplished by utilizing simultaneous, on-line, and continuous monitoring of mechanical performance parameters and the exchange kinetics of 42K, 85Sr, 133Ba, 47Ca and 45Ca in isolated perfused septa of rabbits and cultured heart cells of rats.